Merge branch 'rs/ref-transaction-rename' into jch

Merge branch 'rs/ref-transaction-rename' into jch

Follow-up on rs/ref-transaction series to make renaming a ref
transactional (i.e. "delete old and create new" should not leave
an in-between state behind when it fails).

No more nitpicks and better design suggestions?

* rs/ref-transaction-rename:
  refs.c: rollback the lockfile before we die() in repack_without_refs
  refs.c: update rename_ref to use a transaction
  refs.c: use packed refs when deleting refs during a transaction
  refs.c: return error instead of dying when locking fails during transaction
  refs.c: allow passing raw git_committer_info as email to _update_reflog

# Conflicts:
# 	refs.c